The present invention relates to magnetoresistive heads and more particularly to a method and system for providing electrostatic discharge protection for devices using a flex-on suspension, trace-suspension assembly, or a cable-on suspension.
Magnetoresistive (MR) heads are increasingly popular for use in reading data from magnetic recording media. MR heads utilize an MR sensor in order to read data from the magnetic recording media. The MR sensor is typically either an anisotropic magnetoresistive (AMR) sensor or a giant magnetoresistive (GMR) sensor. In order to read data using the MR head, current is driven through the MR sensor. The change in resistance of the sensor due to the magnetic field of each bit stored in the recording media is translated into a signal. Thus, the stored data is read.
In order to use the MR head in a disk drive, the head is attached to a metal arm, or suspension, that can be used to suspend the head above the recording media. In order to function, electrical connection must be made to the MR sensor in the MR head. A conventional suspension assembly, therefore, includes a twisted pair of wires mechanically connected to the metal arm. Each wire in the twisted pair is connected to the MR sensor. Thus, electrical connection is made to the MR sensor, allowing current to be driven through the MR sensor. The combination of the head and suspension is known as a head-gimbal assembly. Sets of head-gimbal assemblies are stacked together to form a head-stack assembly. The head-gimbal assembly or head-stack assembly can be installed in a disk drive for use in reading recording media.
As the areal density of the bits stored in the recording media increases, the sizes of the MR sensor and MR head decrease. Thus, coupling the wires to the MR head while maintaining quality, performance, and manufacturability becomes increasingly difficult. As a result, other conventional suspension assemblies which do not use wires have been developed. Such conventional wireless suspension assemblies use other materials, such as polyimide materials (e.g. kapton), in a flat thin architecture. For example, Read-Rite Corp. of Milpitas, Calif. has developed flex-on-suspension (FOS) technology. Similarly, trace suspension assembly (TSA) and cable on suspension (COS) technology have been developed. Conventional wireless suspension assemblies using conventional FOS, conventional TSA, and conventional COS do not use a twisted pair of wires to provide electrical connection to the head. Instead, the conventional wireless suspension assemblies use leads supported by an insulating film. Typically, the insulating film is made from a polyimide material, such as kapton. Two leads are typically sandwiched between two layers of kapton. Both conventional FOS and conventional TSA utilize such a suspension assembly. However, the shape of the kapton-lead sandwich of the conventional FOS differs from the shape of the kapton-lead sandwich in the conventional TSA.
Although the conventional FOS, conventional TSA, and conventional COS suspension assemblies aid in manufacturing high areal density head-gimbal assemblies, conventional suspension assemblies such as conventional FOS and TSA suffer from failures. It has been determined that these failures are due to tribocharging of the kapton, which causes electrostatic discharge (ESD) damage. During fabrication, the kapton is subject to tribocharging. The tribocharge in the kapton traps an opposite charge in the leads near the location of the tribocharge. Thus, an excess charge that is free to move remains in the leads. If the leads are contacted, which typically happens during fabrication, the excess charge can flow through the leads and, therefore, the MR sensor. This flow of charge can destroy the MR sensor. In the alternative, the excess charge may reside on the MR sensor. In such a case, the charge at the MR sensor may jump to another portion of the MR head, such as the shield or substrate. This spark may also destroy the MR sensor. Thus, in head-gimbal assemblies using FOS or TSA, the MR sensor is relatively likely to be destroyed during fabrication.
Accordingly, what is needed is a system and method for providing a head-gimbal assembly using technology such as FOS, TSA, and COS and which is less subject to failure. The present invention addresses such a need.
The present invention provides a method and system for protecting a suspension assembly, for example for a flex-on-suspension or trace suspension assembly. The suspension assembly is for use with a magnetoresistive (MR) head including an MR sensor. The MR sensor has a first end and a second end. The method and system comprise providing a first lead coupled with the first end of the MR sensor and providing a second lead coupled with the second end of the MR sensor. The method and system further comprise providing an insulating film supporting a first portion of the first lead and a second portion of the second lead. In one aspect, the method and system also comprise providing a resistor coupled with the first lead, the resistor being sufficiently large to damp a transient current in the MR sensor. In another aspect, the method and system comprise providing a pair of resistors. Each resistor is coupled to one of the leads. The resistors are also coupled in parallel. Each resistor is large enough to damp the transient current in the MR sensor.
According to the system and method disclosed herein, the present invention can damp transient currents due to tribocharging. When the resistor or pair of resistors is coupled to ground, the system and method can also provide a path for charge due to tribocharging to be dissipated, thereby reducing or eliminating excess charge on the MR sensor. Consequently, the possibility of the damage or destruction of the MR sensor is reduced or eliminated.